Stacked source-drain-gate connection and process for forming such

ABSTRACT

A device is disclosed. The device includes a first epitaxial region, a second epitaxial region, a first gate region between the first epitaxial region and a second epitaxial region, a first dielectric structure underneath the first epitaxial region, a second dielectric structure underneath the second epitaxial region, a third epitaxial region underneath the first epitaxial region, a fourth epitaxial region underneath the second epitaxial region, and a second gate region between the third epitaxial region and a fourth epitaxial region and below the first gate region. The device also includes, a conductor via extending from the first epitaxial region, through the first dielectric structure and the third epitaxial region, the conductor via narrower at an end of the conductor via that contacts the first epitaxial region than at an opposite end.

TECHNICAL FIELD

Embodiments of the disclosure pertain to devices having stackedsource-drain-gate connections and, in particular, to devices havingstacked source-drain-gate connections formed from the backside of thedevice.

BACKGROUND

Electrically connecting the source-drain regions of two or moremonolithically stacked transistors is required as part of thefabrication of many types of electronic circuits. Some solutions to thechallenges presented by such involve routing metal around the source anddrain regions of the transistors (e.g., wrap-around constructions orthrough interstitial isolation regions) or etching a via through the topside source-drain epitaxial regions. However, wrap-around vias requiresignificantly more area and can result in a substantially larger diefootprint. Moreover, etching through the top side epitaxial region cancause unwanted strain relaxation or loss of body volume. In addition,forming vias to the gate and source-drain regions of a device can causea significant increase in capacitive coupling between the gate andsource-drain regions of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a transistor of a previous approach.

FIG. 2A illustrates a device with a stacked source-drain-gate structureaccording to an embodiment.

FIG. 2B illustrates a device with a stacked source-drain-gate structureaccording to an embodiment.

FIG. 2C illustrates a device with a stacked source-drain-gate structureaccording to an embodiment.

FIG. 2D illustrates a device with a source-drain-gate structure thatprovides reduced parasitic capacitance according to an embodiment.

FIGS. 3A-3E illustrate cross-sections of a semiconductor structure atstages during the process of fabricating a device with a stackedsource-drain-gate structure according to an embodiment.

FIG. 4 illustrates a flowchart of a process of fabricating a device witha stacked source-drain-gate structure according to an embodiment.

FIG. 5 illustrates a computing device in accordance with oneimplementation of an embodiment.

FIG. 6 illustrates an interposer that includes one or more embodiments.

DESCRIPTION OF THE EMBODIMENTS

A device with a stacked source-drain-gate structure is described. Itshould be appreciated that although embodiments are described hereinwith reference to example stacked source-drain-gate structureimplementations, the disclosure is more generally applicable to stackedsource-drain-gate structure implementations as well as other typestacked source-drain-gate structure implementations. In the followingdescription, numerous specific details are set forth, such as specificintegration and material regimes, in order to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to one skilled in the art that embodiments of the presentdisclosure may be practiced without these specific details. In otherinstances, well-known features, such as integrated circuit designlayouts, are not described in detail in order to not unnecessarilyobscure embodiments of the present disclosure. Furthermore, it is to beappreciated that the various embodiments shown in the Figures areillustrative representations and are not necessarily drawn to scale.

Certain terminology may also be used in the following description forthe purpose of reference only, and thus are not intended to be limiting.For example, terms such as “upper”, “lower”, “above”, and “below” referto directions in the drawings to which reference is made. Terms such as“front”, “back”, “rear”, and “side” describe the orientation and/orlocation of portions of the component within a consistent but arbitraryframe of reference which is made clear by reference to the text and theassociated drawings describing the component under discussion. Suchterminology may include the words specifically mentioned above,derivatives thereof, and words of similar import.

Electrically connecting the source-drain regions of two or moremonolithically stacked transistors is required as part of thefabrication of many types of electronic circuits. Some solutions to thechallenges presented by such involve routing metal around the source anddrain regions of the transistors (e.g., wrap-around constructions orthrough interstitial isolation regions) or etching a via through the topside source-drain epitaxial regions. However, wrap-around vias requiresignificantly more area thus can result in a substantially larger diefootprint. Moreover, etching through the top side epitaxial region cancause unwanted strain relaxation or loss of body volume. In addition,forming vias to the gate and source-drain regions of a device can causea significant increase in capacitive coupling between the gate andsource-drain regions of the device.

An approach that addresses the shortcomings of previous approaches isdisclosed and described herein. In an embodiment, the source-drainregions of two or more monolithically stacked transistors can beelectrically connected from the back side of the transistors. Forexample, in an embodiment, a via can be formed through a bottomsource-drain epitaxial region (e.g., doped Si or SiGe in an embodiment)and any dielectric isolation material of the monolithically stackedtransistors (two or more layers). In an alternative embodiment, a viacan be formed on a single-layer device (e.g., CMOS) if a front-to-backvia is needed and the etch cannot be integrated during front sideprocessing. In an embodiment, using such processes, a low resistivity,high contact area contact can be vertically formed between stackeddevices. In an embodiment, epitaxial source-drain growth does not needto be seeded from a metal conductor.

Forming the contact to the gate from the backside and to thesource-drain from the front-side in either a stacked architecture or asingle-strata architecture can minimize the capacitive coupling betweenthe gate and source-drain contacts. The analogous case of formingbackside source-drain contacts and front-side gate contacts is analternative embodiment that can in a similar manner reduce thiscapacitance. In an embodiment, the reduction of capacitive couplingcapacitance enables faster switching and/or lower power consumption.

FIG. 1 illustrates a transistor 100 of a previous approach. In FIG. 1,the transistor 100 includes (shallow trench isolation) STI layer 101,first epitaxial region 103, contact metal 105, interlayer dielectric(ILD) 107, conductor via 109, conductor via 111, conductor via 113,contact metal 115, second epitaxial region 117, gate spacer 119 and gatemetal 121.

Referring to FIG. 1, metal conductor via 109 is connected to firstepitaxial region 103 through contact metal 105, metal conductor via 111is connected to gate metal 121 and transistor channel (not shown), andmetal conductor via 113 is connected to second epitaxial region 117through contact metal 115. The metal conductor via 109, the metalconductor via 111 and the metal conductor via 113 are separated by ILD107. The capacitors (see FIG. 1) that are created by the separation ofthe metal conductor via 109, the metal conductor via 111 and the metalconductor via 113 by the dielectric ILD 107 material generates a largeparasitic capacitance that degrades the performance of the transistor101. In particular, the source-to-gate and gate-to-drain capacitivecoupling that is exhibited reduces switching speed and/or causesincreases in transistor power consumption.

FIG. 2A illustrates a device with a stacked source-drain-gate structure229 according to an embodiment. It should be appreciated that FIG. 2Ashows the completed structure 200 after it has been flipped and theformation of a via completed. As such, the orientation of the structure200 is shown as rotated by 180 degrees and is the basis for thereference herein to “bottom” structures that are shown at the top of thestructure 200 and vice versa. In an embodiment, as shown in FIG. 2A, thedevice with stacked source-drain-gate 229 can include via 201, bottomepitaxial structure 203, spacer 205, spacer 207, bottom gate conductor209, bottom contact conductor 211, bottom epitaxial structure 213,dielectric structure 215, dielectric structure 217, top epitaxialstructure 219, top epitaxial structure 221, top gate conductor 223, topcontact conductor 225, and top contact conductor 227. In FIG. 2A thedrawing to the left is a perspective view with a cutline perpendicularto the channel through the source-drain region. The drawing to the rightis a perspective view with a cutline parallel to the channel.

Referring to FIG. 2A, in an embodiment, conductor via 201 can be formedon epitaxial structure 221 and can extend through dielectric structure217, epitaxial structure 203 and spacer 205. In an embodiment, theconductor via 201 can have a width from 6 to 25 nm. In otherembodiments, the conductor via 201 can have other widths. In anembodiment, the conductor via 201 can have a length from 5 to 50 nm. Inother embodiments, the conductor via 201 can have other lengths. In anembodiment, the conductor via 201 can be tapered. In particular, theconductor via 201 can be narrower at an end adjacent the epitaxialstructure 221 than it is at its opposite end. In an embodiment, thebottom epitaxial structure 203 can be formed between dielectricstructure 217 and spacer 205. In an embodiment, the bottom epitaxialstructure 203 can have a length from 5 to 50 nm. In other embodiments,the bottom epitaxial structure 203 can have other lengths. In anembodiment, the dielectric structure 217 can be formed above the bottomepitaxial structure 203 and below the top epitaxial structure 221 (inright-side-up orientation). In an embodiment, the spacer 205 can beformed below the epitaxial structure 203 and can surround a portion ofthe conductor via 201 (in right-side-up orientation). In an embodiment,the spacers 207 can be formed adjacent the sides of the top gateconductor 223 and the bottom gate conductor 209. In an embodiment, thebottom gate structure 209 can be formed between the spacers 207. In anembodiment, the bottom contact conductor 211 can be formed below thebottom epitaxial structure 213 (in right-side-up orientation). In anembodiment, the bottom epitaxial structure 213 can be formed above thebottom contact conductor 211 (in right-side-up orientation) and adjacenta portion of the spacers 207. In an embodiment, the length of theepitaxial structure 213 can be from 5 to 50 nm. In other embodiments,the epitaxial structure 213 can have other lengths. In an embodiment,the dielectric structure 215 can be formed above the bottom epitaxialstructure 213 and below the top epitaxial structure 219 (inright-side-up orientation). The top epitaxial structure 219 can beformed below the top contact conductor 225 and above the dielectricstructure 215 (in right-side-up orientation). In an embodiment, thelength of the epitaxial structure 219 can be from 5 to 50 nm. In otherembodiments, the epitaxial structure 219 can have other lengths. In anembodiment, the top epitaxial structure 221 can be formed under the topcontact conductor 227 and above dielectric structure 217 (inright-side-up orientation). In an embodiment, the length of theepitaxial structure 221 can be from 5 to 50 nm. In other embodiments,the epitaxial structure 221 can have other lengths. In an embodiment,the top gate conductor 223 can be formed above the bottom gate conductor209 (in right-side-up orientation). In an embodiment, the top contactconductor 225 can be formed above the epitaxial structure 219 (inright-side-up orientation) and adjacent the spacer 207. In anembodiment, the top contact conductor 227 can be formed above theepitaxial structure 221 (in right-side-up orientation) and adjacent thespacer 207.

In an embodiment, through conductor via 201 can be formed from TiN, W,or TaN. In other embodiments, the through conductor via 201 can beformed from other materials. In an embodiment, the bottom epitaxialstructure 203 can be formed from Si or SiGe. In other embodiments, thebottom epitaxial structure 203 can be formed from other materials. In anembodiment, the spacer 205 can be formed from SiN or SiO₂. In otherembodiments, the spacer 205 can be formed from other materials. In anembodiment, the spacers 207 can be formed from SiN or SiO₂. In otherembodiments, the spacers 207 can be formed from other materials. In anembodiment, the bottom gate conductor 209 can be formed from TiN, W, orTaN. In other embodiments, the bottom gate conductor 209 can be formedfrom other materials. In an embodiment, the bottom contact conductor 211can be formed from TiN, W, or TaN. In other embodiment, the bottomcontact conductor 211 can be formed from other materials. In anembodiment, the bottom epitaxial structure 213 can be formed from Si orSiGe. In other embodiments, the bottom epitaxial structure 213 can beformed from other materials. In an embodiment, the dielectric structure215 can be formed from SiN or SiO₂. In other embodiments, the dielectricstructure 215 can be formed from other materials. In an embodiment, thedielectric structure 217 can be formed from SiN or Sift. In otherembodiments, the dielectric structure 217 can be formed from othermaterials. In an embodiment, the top epitaxial structure 219 can beformed from Si or SiGe. In other embodiments, the top epitaxialstructure 219 can be formed from other materials. In an embodiment, thetop epitaxial structure 221 can be formed from Si or SiGe. In otherembodiments, the top epitaxial structure 221 can be formed from othermaterials. In an embodiment, the top gate conductor 223 can be formedfrom TiN, W, or TaN. In other embodiments, the top gate conductor 223can be formed from other materials. In an embodiment, the top contactconductor 225 can be formed from TiN, W, or TaN. In other embodimentsthe top contact conductor 225 can be formed from other materials. In anembodiment, the top contact conductor 227 can be formed from TiN, W, orTaN. In other embodiments, the top contact conductor 227 can be formedfrom other materials.

In operation, because of the low resistivity, high contact area formedbetween stacked devices of the stacked source-drain-gate structure 200shown in FIG. 2A, the capacitive coupling between the gate conductors209 and 223 and the source/drain contacts (e.g., 211, 225 and 227) isminimized and, a reduction in parasitic capacitances relative toprevious approaches is realized (see FIG. 1). It should be appreciatedthat this reduction in parasitic capacitance directly impacts theperformance of the transistor. In particular, the reduced parasiticcapacitance enables faster switching and/or lower power consumption ascompared to previous approaches.

FIG. 2B illustrates a device with stacked source-drain-gate structure200 according to an embodiment. In the FIG. 2B embodiment, the spacermaterial can be deposited above the semiconductor structure and can beshaped to form spacers 231 that shadow the epitaxial sidewalls that arelocated above both the epitaxial region 203 and the epitaxial region213. In contrast to the embodiment shown in FIG. 2A, the FIG. 2Bembodiment can include the spacers 231 above the epitaxial regions 203and 213. And, can include the contact conductor 211 formed in a via(shown at right) defined by the spacers 231. In FIG. 2B the drawing tothe left is a perspective view with a cutline perpendicular to thechannel. In FIG. 2B, the drawing to the right is a perspective view witha cutline parallel to the channel through the source-drain region.

FIG. 2C illustrates a device with stacked source-drain-gate structure200 according to an embodiment. In the FIG. 2C embodiment, the spacermaterial can be deposited above the semiconductor structure and can beshaped to form spacers 231 (similar to those of FIG. 2B) that shadow theepitaxial sidewalls that are located above both the epitaxial region 203and the epitaxial region 213. In contrast to the embodiment shown inFIG. 2A, in FIG. 2C, the spacers 231 shown on the left facilitates athrough etch that extends through the epitaxial region 213. In anembodiment, the conductor that is formed in the via formed by thethrough etch is used to increase contact area and decrease contactresistance. In an embodiment, the spacers 231 that form the throughisolation via for the etch can be lithographically defined. In otherembodiments, the spacers 231 that form the through isolation via for theetch can be defined in other manners.

FIGS. 2B and 2C show a completed assembly with a conductor via that isformed after the wafer has been flipped and the bottom side of thetransistors exposed. It should be noted that the front sideinterconnects are fully fabricated at this point. In FIGS. 2B and 2C,the top epitaxial region and the bottom epitaxial region correspond to afront side or top and a back side or bottom respectively (e.g., beforethe wafer is flipped). The process that is performed to build thisassembly is shown in FIGS. 3A-3E. FIGS. 2B and 2C include verticalcontacts that extend between stacked transistors. Referring to FIGS. 2Band 2C, the left image and right image are cross sections that are cutperpendicular to, and parallel to, the device channel, respectively. Thelocations of these cross sections are shown by the dashed arrows.

FIG. 2D illustrates a single layer transistor according to anembodiment. In FIG. 2D, the transistor includes STI 251, conductor via253, conductor via 255, spacers 257, conductor contact 259, epitaxialregion 261, dielectric structure 263, gate spacers 265, ILD 267,dielectric structure 269, epitaxial region 271, conductor contact 275,spacers 273, gate conductor 277, and via to gate 279.

Referring to FIG. 2D, in an embodiment, conductor via to source-drainregion 253 can be connected to first epitaxial region 261 throughconductor contact 259. In an embodiment, conductor via to source-drainregion 255 can be connected to second epitaxial region 271 throughconductor contact 275. In an embodiment, conductor via to gate 279 canbe connected to gate conductor 277. In an embodiment, the conductor viato gate 277 and the conductor vias to the source-drain regions 253 and255 can be on opposite sides of the semiconductor structure. Thisarrangement reduces the generation of parasitic capacitance that candegrade the performance of the transistor when these structures arelocated side by side on the same side of the structure (see FIG. 1). Inparticular, as described herein, the decrease in source-to-gate andgate-to-drain capacitive coupling increases switching speed and/orreduces transistor power consumption.

FIGS. 3A-3E shows cross-sections of a semiconductor structure at stagesduring the fabrication of a stacked source-drain-gate device accordingto an embodiment. Referring to FIG. 3A, after a plurality of operationsthe semiconductor structure includes substrate 301, STI 303, epitaxialstructure 305, dielectric structure 307, epitaxial structure 309,contact conductor 311, STI 313, epitaxial structure 315, dielectricstructure 317, epitaxial structure 319, contact conductor 321, spacer323, spacer 325, gate conductor 327, gate conductor 329, and isolationwall 330. In FIGS. 3A-3E the drawing at the top of each figure is aperspective view with a cutline perpendicular to the channel through thesource-drain region. Moreover, the drawing at the bottom of each figureis a perspective view with a cutline parallel to the channel.

Referring to FIG. 3B, subsequent to one or more operations that resultin a cross-section of the structure shown in FIG. 3A, the wafer isflipped and the bottom of the stacked devices (e.g., transistors) areexposed by the removal of the substrate 301.

Referring to FIG. 3C, subsequent to one or more operations that resultin the cross-section shown in FIG. 3B, the STI material 303 and 313 isremoved and spacers 331 are formed for via formation. In an embodiment,the STI material can be removed by etching processes. In an embodiment,the STI material can be removed by isotropic, anisotropic, plasmaetching, ion milling or sputter etching. In other embodiments, the STImaterial can be removed in other manners. In an embodiment, the spacers331 can be formed by patterning or deposition processes. In otherembodiments, the spacers can be formed in other manners.

Referring to FIG. 3D, subsequent to one or more operations that resultin the cross-section shown in FIG. 3C, a via is formed (the space intowhich conductor material is formed). In an embodiment, the via can beformed by patterning and etching processes. In an embodiment, the via333 can be formed by isotropic, anisotropic, plasma etching, ion millingor sputter etching. In other embodiments, the via can be formed in othermanners.

Referring to FIG. 3E, subsequent to one or more operations that resultin the cross-section shown in FIG. 3D, the conductor via 335 and theother back side contacts are formed. In an embodiment, the conductor via335 can be formed by filling the space shown in FIG. 3D. In anembodiment, the conductor via 335 can be formed by atomic layerdeposition (ALD), physical vapor deposition (PVD), chemical vapordeposition (CVD), electrochemical deposition (ECD), or molecular beamepitaxy (MBE). In other embodiments, the conductor via 335 can be formedin other manners.

It should be appreciated that the sequence shown in FIG. 3A-3E, beginssubsequent to the completion of front side processing. FIG. 3B shows thestructure subsequent to the device wafer being flipped and the bottomsof the transistors exposed. As shown in FIG. 3C, after thesub-source-drain material (e.g., STI) is removed, and a spacer isdeposited and etched in the regions in which the via is to be formed,the via is lithographically patterned and then etched through the bottomepitaxial and dielectric isolation structures as shown in FIG. 3D. In anembodiment, the sidewalls of the epitaxial material is shadowed by thespacer that is deposited in operations that result in the cross-sectionshown in FIG. 3C. In FIG. 3E, the via and other back side source-draincontacts are metallized. Thereafter, further processing can beperformed.

In an embodiment, the epitaxial boundary is formed in the same plane asthe spacer material. In an embodiment, this characteristic is visible inthe structure using visual analysis techniques. In an embodiment, themonolithic structure described with reference to FIGS. 2A-2C consist oftwo transistor layers. However, it is equally applicable to stacks ofany number of layers (including single layers). In an embodiment, theprocess described herein is equally applicable to channels of any shape(e.g. fins, nanowires, nanoribbons, etc.). In the example process ofFIGS. 3A-3E, the via shadowing spacer is formed in the source-drainregions that have the via. In other embodiments the via shadowing spacercan be formed in each source-drain region. In the example process ofFIGS. 3A-3E, the bottom epitaxial region is etched in the source-drainregion where a via is to be formed therein. In other embodiments, thebottom epitaxial regions can be etched in each source-drain region toimprove bottom contact area. In such embodiments, the dielectricisolation between the top and bottom epitaxial regions can be etched toform the stacked source-drain connection. FIGS. 3A-3E shows the mannerin which a source-drain contact can be formed from the backside of astacked monolithic structure. In other embodiments, the source-draincontacts can be formed from either the top or the bottom side and thegate contact can be formed from the side opposite that upon which thesource-drain contacts are formed.

FIG. 4 illustrates a flowchart of a method for forming a transistor witha stacked source-drain-gate connection according to an embodiment.Referring to FIG. 4, the method includes, at 401, forming a firstepitaxial region. At 403, forming a second epitaxial region. At 405,forming a first gate region between the first epitaxial region and asecond epitaxial region. At 407, forming a first dielectric structureunderneath the first epitaxial region. At 409, forming a seconddielectric structure underneath the second epitaxial region. At 411,forming a third epitaxial region underneath the first epitaxial region.At 413, forming a fourth epitaxial region underneath the secondepitaxial region. At 415, forming a second gate region between the thirdepitaxial region and a fourth epitaxial region and below the first gateregion. At 417, forming a conductor via extending from the firstepitaxial region. In an embodiment, the conductor via extends throughthe first dielectric structure and the third epitaxial region. In anembodiment, the conductor via is narrower at an end of the conductor viathat contacts the first epitaxial region than at an opposite end of theconductor via.

Implementations of embodiments of the invention may be formed or carriedout on a substrate, such as a semiconductor substrate. In oneimplementation, the semiconductor substrate may be a crystallinesubstrate formed using a bulk silicon or a silicon-on-insulatorsubstructure. In other implementations, the semiconductor substrate maybe formed using alternate materials, which may or may not be combinedwith silicon, that include but are not limited to germanium, indiumantimonide, lead telluride, indium arsenide, indium phosphide, galliumarsenide, indium gallium arsenide, gallium antimonide, or othercombinations of group III-V or group IV materials. Although a fewexamples of materials from which the substrate may be formed aredescribed here, any material that may serve as a foundation upon which asemiconductor device may be built falls within the spirit and scope ofthe present invention.

A plurality of transistors, such as metal-oxide-semiconductorfield-effect transistors (MOSFET or simply MOS transistors), may befabricated on the substrate. In various implementations of theinvention, the MOS transistors may be planar transistors, nonplanartransistors, or a combination of both. Nonplanar transistors includeFinFET transistors such as double-gate transistors and tri-gatetransistors, and wrap-around or all-around gate transistors such asnanoribbon and nanowire transistors. Although the implementationsdescribed herein may illustrate only planar transistors, it should benoted that the invention may also be carried out using nonplanartransistors.

Each MOS transistor includes a gate stack formed of at least two layers,a gate dielectric layer and a gate electrode layer. The gate dielectriclayer may include one layer or a stack of layers. The one or more layersmay include silicon oxide, silicon dioxide (SiO₂) and/or a high-kdielectric material. The high-k dielectric material may include elementssuch as hafnium, silicon, oxygen, titanium, tantalum, lanthanum,aluminum, zirconium, barium, strontium, yttrium, lead, scandium,niobium, or zinc. Examples of high-k materials that may be used in thegate dielectric layer include, but are not limited to, hafnium oxide,hafnium silicon oxide, lanthanum oxide, lanthanum aluminum oxide,zirconium oxide, zirconium silicon oxide, tantalum oxide, titaniumoxide, barium strontium titanium oxide, barium titanium oxide, strontiumtitanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalumoxide, or lead zinc niobate. In some embodiments, an annealing processmay be carried out on the gate dielectric layer to improve its qualitywhen a high-k material is used.

The gate electrode layer is formed on the gate dielectric layer and mayconsist of at least one P-type workfunction metal or N-type workfunctionmetal, depending on whether the transistor is to be a PMOS or an NMOStransistor. In some implementations, the gate electrode layer mayconsist of a stack of two or more metal layers, where one or more metallayers are workfunction metal layers and at least one metal layer is afill metal layer.

For a PMOS transistor, metals that may be used for the gate electrodeinclude, but are not limited to, ruthenium, palladium, platinum, cobalt,nickel, or conductive metal oxides, e.g., ruthenium oxide. A P-typemetal layer will enable the formation of a PMOS gate electrode with aworkfunction that is between about 4.9 eV and about 5.2 eV. For an NMOStransistor, metals that may be used for the gate electrode include, butare not limited to, hafnium, zirconium, titanium, tantalum, aluminum,alloys of these metals, or carbides of these metals such as hafniumcarbide, zirconium carbide, titanium carbide, tantalum carbide, oraluminum carbide. An N-type metal layer will enable the formation of anNMOS gate electrode with a workfunction that is between about 3.9 eV andabout 4.2 eV.

In some implementations, the gate electrode may consist of a “U”-shapedstructure that includes a bottom portion substantially parallel to thesurface of the substrate and two sidewall portions that aresubstantially perpendicular to the top surface of the substrate. Inanother implementation, at least one of the metal layers that form thegate electrode may simply be a planar layer that is substantiallyparallel to the top surface of the substrate and does not includesidewall portions substantially perpendicular to the top surface of thesubstrate. In further implementations of the invention, the gateelectrode may consist of a combination of U-shaped structures andplanar, non-U-shaped structures. For example, the gate electrode mayconsist of one or more U-shaped metal layers formed atop one or moreplanar, non-U-shaped layers.

In some implementations of the invention, a pair of sidewall spacers maybe formed on opposing sides of the gate stack that bracket the gatestack. The sidewall spacers may be formed from a material such assilicon nitride, silicon oxide, silicon carbide, silicon nitride dopedwith carbon, or silicon oxynitride. Processes for forming sidewallspacers are well known in the art and generally include deposition andetching process steps. In an alternate implementation, a plurality ofspacer pairs may be used, for instance, two pairs, three pairs, or fourpairs of sidewall spacers may be formed on opposing sides of the gatestack.

As is well known in the art, source and drain regions are formed withinthe substrate adjacent to the gate stack of each MOS transistor. Thesource and drain regions are generally formed using either animplantation/diffusion process or an etching/deposition process. In theformer process, dopants such as boron, aluminum, antimony, phosphorous,or arsenic may be ion-implanted into the substrate to form the sourceand drain regions. An annealing process that activates the dopants andcauses them to diffuse further into the substrate typically follows theion implantation process. In the latter process, the substrate may firstbe etched to form recesses at the locations of the source and drainregions. An epitaxial deposition process may then be carried out to fillthe recesses with material that is used to fabricate the source anddrain regions. In some implementations, the source and drain regions maybe fabricated using a silicon alloy such as silicon germanium or siliconcarbide. In some implementations the epitaxially deposited silicon alloymay be doped in situ with dopants such as boron, arsenic, orphosphorous. In further embodiments, the source and drain regions may beformed using one or more alternate semiconductor materials such asgermanium or a group III-V material or alloy. And, in furtherembodiments, one or more layers of metal and/or metal alloys may be usedto form the source and drain regions.

One or more interlayer dielectrics (ILD) are deposited over the MOStransistors. The ILD layers may be formed using dielectric materialsknown for their applicability in integrated circuit structures, such aslow-k dielectric materials. Examples of dielectric materials that may beused include, but are not limited to, silicon dioxide (SiO₂), carbondoped oxide (CDO), silicon nitride, organic polymers such asperfluorocyclobutane or polytetrafluoroethylene, fluorosilicate glass(FSG), or organosilicates such as silsesquioxane, siloxane, ororganosilicate glass. The ILD layers may include pores or air gaps tofurther reduce their dielectric constant.

FIG. 5 illustrates a computing device 500 in accordance with oneimplementation of the invention. The computing device 500 houses a board502. The board 502 may include a number of components, including but notlimited to a processor 504 and at least one communication chip 506. Theprocessor 504 is physically and electrically coupled to the board 502.In some implementations the at least one communication chip 506 is alsophysically and electrically coupled to the board 502. In furtherimplementations, the communication chip 506 is part of the processor504.

Depending on its applications, computing device 500 may include othercomponents that may or may not be physically and electrically coupled tothe board 502. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth). In an embodiment, memory and or logic systemsof computing device 500 (such as but not limited to DRAM and/or DRAMthat is embedded in logic) can include devices such as transistorstructures described herein with reference to FIGS. 2A-2D.

The communication chip 506 enables wireless communications for thetransfer of data to and from the computing device 500. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 506 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 500 may include a plurality ofcommunication chips 506. For instance, a first communication chip 506may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 506 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 504 of the computing device 500 includes an integratedcircuit die packaged within the processor 504. In some implementationsof the invention, the integrated circuit die of the processor includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention. The term “processor” may refer toany device or portion of a device that processes electronic data fromregisters and/or memory to transform that electronic data into otherelectronic data that may be stored in registers and/or memory.

The communication chip 506 also includes an integrated circuit diepackaged within the communication chip 506. In accordance with anotherimplementation of the invention, the integrated circuit die of thecommunication chip includes one or more devices, such as MOS-FETtransistors built in accordance with implementations of the invention.

In further implementations, another component housed within thecomputing device 500 may contain an integrated circuit die that includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention.

In various implementations, the computing device 500 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 500 may be any other electronic device that processes data.

FIG. 6 illustrates an interposer 600 that includes one or moreembodiments of the invention. The interposer 600 is an interveningsubstrate used to bridge a first substrate 602 to a second substrate604. The first substrate 602 may be, for instance, an integrated circuitdie. The second substrate 604 may be, for instance, a memory module, acomputer motherboard, or another integrated circuit die. Generally, thepurpose of an interposer 600 is to spread a connection to a wider pitchor to reroute a connection to a different connection. For example, aninterposer 600 may couple an integrated circuit die to a ball grid array(BGA) 606 that can subsequently be coupled to the second substrate 604.In some embodiments, the first and second substrates 602/604 areattached to opposing sides of the interposer 600. In other embodiments,the first and second substrates 602/604 are attached to the same side ofthe interposer 600. And in further embodiments, three or more substratesare interconnected by way of the interposer 600.

The interposer 600 may be formed of an epoxy resin, afiberglass-reinforced epoxy resin, a ceramic material, or a polymermaterial such as polyimide. In further implementations, the interposer600 may be formed of alternate rigid or flexible materials that mayinclude the same materials described above for use in a semiconductorsubstrate, such as silicon, germanium, or other group III-V or group IVmaterials.

The interposer 600 may include metal interconnects 608 and vias 610,including but not limited to through-silicon vias (TSVs) 612. Theinterposer 600 may further include embedded devices 614, including bothpassive and active devices. Such devices include, but are not limitedto, capacitors, decoupling capacitors, resistors, inductors, fuses,diodes, transformers, sensors, or electrostatic discharge (ESD) devices.More complex devices such as radio-frequency (RF) devices, poweramplifiers, power management devices, antennas, arrays, sensors, or MEMSdevices may also be formed on the interposer 600. In accordance withembodiments of the invention, apparatuses or processes disclosed hereinmay be used in the fabrication of interposer 600.

Although specific embodiments have been described above, theseembodiments are not intended to limit the scope of the presentdisclosure, even where only a single embodiment is described withrespect to a particular feature. Examples of features provided in thedisclosure are intended to be illustrative rather than restrictiveunless stated otherwise. The above description is intended to cover suchalternatives, modifications, and equivalents as would be apparent to aperson skilled in the art having the benefit of the present disclosure.

The scope of the present disclosure includes any feature or combinationof features disclosed herein (either explicitly or implicitly), or anygeneralization thereof, whether or not it mitigates any or all of theproblems addressed herein. Accordingly, new claims may be formulatedduring prosecution of the present application (or an applicationclaiming priority thereto) to any such combination of features. Inparticular, with reference to the appended claims, features fromdependent claims may be combined with those of the independent claimsand features from respective independent claims may be combined in anyappropriate manner and not merely in the specific combinationsenumerated in the appended claims.

The following examples pertain to further embodiments. The variousfeatures of the different embodiments may be variously combined withsome features included and others excluded to suit a variety ofdifferent applications.

Example embodiment 1: A device, comprising: a first epitaxial region; asecond epitaxial region; a first gate region between the first epitaxialregion and a second epitaxial region; a first dielectric structureunderneath the first epitaxial region; a second dielectric structureunderneath the second epitaxial region; a third epitaxial regionunderneath the first epitaxial region; a fourth epitaxial regionunderneath the second epitaxial region; a second gate region between thethird epitaxial region and a fourth epitaxial region and below the firstgate region; and a conductor via extending from the first epitaxialregion, through the first dielectric structure and the third epitaxialregion, the conductor via narrower at an end of the conductor via thatcontacts the first epitaxial region than at an opposite end.

Example embodiment 2: The device of example embodiment 1, furthercomprising a second conductor via extending from the second epitaxialregion, through the second dielectric structure and the fourth epitaxialregion.

Example embodiment 3: The device of example embodiment 1 furthercomprising a second conductor via extending from the bottom of thesecond dielectric structure and through the fourth epitaxial region.

Example embodiment 4: The device of example embodiment 1, furthercomprising a second conductor via extending from the bottom of thefourth epitaxial region.

Example embodiment 5: The device of example embodiment 1, 2, 3, or 4wherein the first epitaxial region, the second epitaxial region, thethird epitaxial region and the fourth epitaxial region are source-drainregions.

Example embodiment 6: The device of example embodiment 1, 2, 3, 4, or 5,wherein a width of the first conductor via is tapered to become wider inthe direction extending away from the first epitaxial region.

Example embodiment 7: The device of example embodiment 1, 2, 3, 4, 5, or6, further comprising one or more spacers wherein a plane of the one ormore spacers and an epitaxial boundary of one or more of the first,second, third and fourth epitaxial regions are coplanar.

Example embodiment 8: The device of example embodiment 1, 2, 3, 4, 5, 6,or 7, wherein the width of the first conductor via is from 6 to 25 nm.

Example embodiment 9: The device of example embodiment 1, 2, 3, 4, 5, 6,7, or 8, wherein the length of the first conductor via is from 5 to 50nm.

Example embodiment 10: The device of example embodiment claim 1, 2, 3,4, 5, 6, 7, 8, or 9, wherein the length of first, second, third andfourth epitaxial regions are from 5 to 50 nm.

Example embodiment 11: The device of example embodiment 1, 2, 3, 4, 5,6, 7, 8, 9, or 10, wherein the semiconductor structure includes achannel that includes a fin, nanowire or nanoribbon.

Example embodiment 12: A device, comprising: a first epitaxial region; afirst dielectric structure above the first epitaxial region; a secondepitaxial region; a second dielectric structure above the secondepitaxial region; a first gate region between the first epitaxial regionand a second epitaxial region; a first spacer underneath the firstepitaxial region; a second spacer underneath the second epitaxialregion; a first conductor via extending from the first dielectricstructure through the first epitaxial region and the first spacer; asecond conductor via extending from the bottom surface of the secondepitaxial region and through the second spacer; and a gate contact viaconnected to the gate region on a first side of the device, a firstsource-drain contact via connected to the first conductor via on asecond side of the device, and a second source-drain contact viaconnected to the second conductor via on the second side of the device.

Example embodiment 13: The device of example embodiment 12, furthercomprising a channel that includes a fin, nanowire or nanoribbon.

Example embodiment 14: A system, comprising: one or more processingcomponents; and one or more data storage components, the data storagecomponents including at least one device, the at least one deviceincluding: a first epitaxial region; a second epitaxial region; a firstgate region between the first epitaxial region and a second epitaxialregion; a first dielectric structure underneath the first epitaxialregion; a second dielectric structure underneath the second epitaxialregion; a third epitaxial region underneath the first epitaxial region;a fourth epitaxial region underneath the second epitaxial region; asecond gate region between the third epitaxial region and a fourthepitaxial region and below the first gate region; and a conductor viaextending from the first epitaxial region, through the first dielectricstructure and the third epitaxial region, the conductor via narrower atan end that contacts the first epitaxial region than at an opposite end.

Example embodiment 15. The system of example embodiment 14, furthercomprising a channel that includes a fin, nanowire or nanoribbon.

Example embodiment 16: A method, comprising: flipping a semiconductorstructure having one or more source-drain regions wherein a first sideof the semiconductor structure is exposed; removing an STI layer;forming spacers for one or more vias; forming one or more vias based onthe spacers; and forming a first conductor in the one or more vias thatextends through a first source-drain region on the first side of thesemiconductor structure to contact a first source-drain region on asecond side of the semiconductor structure.

Example embodiment 17: The method of example embodiment 16, wherein thesemiconductor structure is a stacked semiconductor structure having oneor more transistor layers.

Example embodiment 18: The method of example embodiment 16, furthercomprising forming a gate contact on a first side of the stackedsemiconductor structure and forming the first conductor in the one ormore vias on a second side of the stacked semiconductor structure.

Example embodiment 19: The method of example embodiment 16 or 17,wherein a width of the one or more vias is tapered to become wider inthe direction extending away from the source-drain region on the secondside.

Example embodiment 20: The method of example embodiment 16, or 19,wherein a plane of the spacers and an epitaxial boundary of the one ormore source-drain regions are coplanar.

Example embodiment 21: The method of example embodiment 16, 19, or 20,wherein the spacers include spacers that correspond to the one or moresource-drain regions.

Example embodiment 22: The method of example embodiment 16, 19, 20, or21, wherein forming the first conductor includes forming the firstconductor to extend through a dielectric isolation structure of thesemiconductor structure and connect the first source-drain region on thefirst side of the semiconductor structure to the first source-drainregion on the second side of the semiconductor structure.

Example embodiment 23: The method of example embodiment 16, furthercomprising forming a conductor in each of the one or more vias throughspacers corresponding to each source-drain region on the first side ofthe semiconductor structure.

Example embodiment 24: The method of example embodiment 16, furthercomprising forming a second conductor in a second one of the one or morevias to extend through a second source-drain region on the first side ofthe semiconductor structure to contact a second source-drain region on asecond side of the semiconductor structure.

Example embodiment 25: The method of example embodiment 16, furthercomprising forming a second conductor in a second one of the one or morevias to extend through a second source-drain region on the first side ofthe semiconductor structure and contact a dielectric structure thatisolates the first side of the semiconductor structure and the secondside of the semiconductor structure.

Example embodiment 26: The method of example embodiment 16, furthercomprising forming a second conductor in a second one of the one or morevias to contact the surface of a second source-drain region on the firstside of the semiconductor structure.

Example embodiment 27: The method of example embodiment 16, 19, 20, 21,22, 23, 24, 25, or 26, wherein the semiconductor structure includes achannel that includes a fin, nanowire or nanoribbon.

Example embodiment 28: A method, comprising forming a first epitaxialregion; forming a second epitaxial region; forming a first gate regionbetween the first epitaxial region and a second epitaxial region;forming a first dielectric structure underneath the first epitaxialregion; forming a second dielectric structure underneath the secondepitaxial region; forming a third epitaxial region underneath the firstepitaxial region; forming a fourth epitaxial region underneath thesecond epitaxial region; forming a second gate region between the thirdepitaxial region and a fourth epitaxial region and below the first gateregion; and forming a conductor via extending from the first epitaxialregion, through the first dielectric structure and the third epitaxialregion, the conductor via narrower at an end of the conductor via thatcontacts the first epitaxial region than at an opposite end.

Example embodiment 29: The method of example embodiment 28, furthercomprising forming a second conductor via extending from the secondepitaxial region, through the second dielectric structure and the fourthepitaxial region.

Example embodiment 30: The method of example embodiment 28, or 29,further comprising forming a second conductor via extending from thebottom of the second dielectric structure and through the fourthepitaxial region.

Example embodiment 31: The method of example embodiment 28, furthercomprising forming a second conductor via extending from the bottom ofthe fourth epitaxial region.

Example embodiment 32: The method of example embodiment 28, 29, or 30,wherein the first epitaxial region, the second epitaxial region, thethird epitaxial region and the fourth epitaxial region are source-drainregions.

Example embodiment 33: The method of example embodiment 28, 29, 30, or32, wherein a width of the first conductor via is tapered to becomewider in the direction extending away from the first epitaxial region.

Example embodiment 34: The method of example embodiment 28, furthercomprising forming one or more spacers wherein a plane of the one ormore spacers and an epitaxial boundary of one or more of the first,second, third and fourth epitaxial regions are coplanar.

Example embodiment 35: The method of example embodiment 28, 29, 30, 32,or 33, wherein the width of the first conductor via is from 6 to 25 nm.

Example embodiment 36: The method of example embodiment 28, 29, 30, 32,33, or 35, wherein the length of the first conductor via is from 5 to 50nm.

Example embodiment 37: The method of example embodiment 28, 29, 30, 31,32, 35, or 36, wherein the length of first, second, third and fourthepitaxial regions are from 5 to 50 nm.

Example embodiment 38: The method of example embodiment 28, 29, 30, 32,33, 35, or 36, wherein the semiconductor structure includes a channelthat includes a fin, nanowire or nanoribbon.

What is claimed is:
 1. A device, comprising: a first epitaxial region; asecond epitaxial region; a first gate region between the first epitaxialregion and a second epitaxial region; a first dielectric structureunderneath the first epitaxial region; a second dielectric structureunderneath the second epitaxial region; a third epitaxial regionunderneath the first epitaxial region; a fourth epitaxial regionunderneath the second epitaxial region; a second gate region between thethird epitaxial region and a fourth epitaxial region and below the firstgate region; and a conductor via extending from the first epitaxialregion, through the first dielectric structure and the third epitaxialregion, the conductor via narrower at an end of the conductor via thatcontacts the first epitaxial region than at an opposite end.
 2. Thedevice of claim 1, further comprising a second conductor via extendingfrom the second epitaxial region, through the second dielectricstructure and the fourth epitaxial region.
 3. The device of claim 1,further comprising a second conductor via extending from the bottom ofthe second dielectric structure and through the fourth epitaxial region.4. The device of claim 1, further comprising a second conductor viaextending from the bottom of the fourth epitaxial region.
 5. The deviceof claim 1, wherein the first epitaxial region, the second epitaxialregion, the third epitaxial region and the fourth epitaxial region aresource-drain regions.
 6. The device of claim 1, wherein a width of thefirst conductor via is tapered to become wider in the directionextending away from the first epitaxial region.
 7. The device of claim1, further comprising one or more spacers wherein a plane of the one ormore spacers and an epitaxial boundary of one or more of the first,second, third and fourth epitaxial regions are coplanar.
 8. The deviceof claim 1, wherein the width of the first conductor via is from 6 to 25nm.
 9. The device of claim 1, wherein the length of the first conductorvia is from 5 to 50 nm.
 10. The device of claim 1, wherein the length offirst, second, third and fourth epitaxial regions are from 5 to 50 nm.11. The device of claim 1, further comprising a channel that includes afin, nanowire or nanoribbon.
 12. A device, comprising: a first epitaxialregion; a first dielectric structure above the first epitaxial region; asecond epitaxial region; a second dielectric structure above the secondepitaxial region; a first gate region between the first epitaxial regionand a second epitaxial region; a first spacer underneath the firstepitaxial region; a second spacer underneath the second epitaxialregion; a first conductor via extending from the first dielectricstructure through the first epitaxial region and the first spacer; asecond conductor via extending from the bottom surface of the secondepitaxial region and through the second spacer; and a gate contact viaconnected to the gate region on a first side of the device, a firstsource-drain contact via connected to the first conductor via on asecond side of the device, and a second source-drain contact viaconnected to the second conductor via on the second side of the device.13. The device of claim 12, further comprising a channel that includes afin, nanowire or nanoribbon.
 14. A system, comprising: one or moreprocessing components; and one or more data storage components, the datastorage components including at least one device, the at least onedevice including: a first epitaxial region; a second epitaxial region; afirst gate region between the first epitaxial region and a secondepitaxial region; a first dielectric structure underneath the firstepitaxial region; a second dielectric structure underneath the secondepitaxial region; a third epitaxial region underneath the firstepitaxial region; a fourth epitaxial region underneath the secondepitaxial region; a second gate region between the third epitaxialregion and a fourth epitaxial region and below the first gate region;and a conductor via extending from the first epitaxial region, throughthe first dielectric structure and the third epitaxial region, theconductor via narrower at an end that contacts the first epitaxialregion than at an opposite end.
 15. The system of claim 14, furthercomprising a channel that includes a fin, nanowire or nanoribbon.
 16. Amethod, comprising: flipping a semiconductor structure having one ormore source-drain regions wherein a first side of the semiconductorstructure is exposed; removing an (STI) shallow trench isolation layer;forming spacers for one or more vias; forming one or more vias based onthe spacers; and forming a first conductor in the one or more vias thatextends through a first source-drain region on the first side of thesemiconductor structure to contact a first source-drain region on asecond side of the semiconductor structure.
 17. The method of claim 16,wherein the semiconductor structure is a stacked semiconductor structurehaving one or more transistor layers.
 18. The method of claim 16,further comprising forming a gate contact on a first side of the stackedsemiconductor structure and forming the first conductor in the one ormore vias on a second side of the stacked semiconductor structure. 19.The method of claim 16, wherein a width of the one or more vias istapered to become wider in the direction extending away from thesource-drain region on the second side.
 20. The method of claim 16,wherein a plane of the spacers and an epitaxial boundary of the one ormore source-drain regions are coplanar.
 21. The method of claim 16,wherein the spacers include spacers that correspond to the one or moresource-drain regions.
 22. The method of claim 16, wherein forming thefirst conductor includes forming the first conductor to extend through adielectric isolation structure of the semiconductor structure andconnect the first source-drain region on the first side of thesemiconductor structure to the first source-drain region on the secondside of the semiconductor structure.
 23. The method of claim 16, furthercomprising forming a conductor in each of the one or more vias throughspacers corresponding to each source-drain region on the first side ofthe semiconductor structure.
 24. The method of claim 16, furthercomprising forming a second conductor in a second one of the one or morevias to extend through a second source-drain region on the first side ofthe semiconductor structure to contact a second source-drain region on asecond side of the semiconductor structure.
 25. The method of claim 16,further comprising forming a second conductor in a second one of the oneor more vias to extend through a second source-drain region on the firstside of the semiconductor structure and contact a dielectric structurethat isolates the first side of the semiconductor structure and thesecond side of the semiconductor structure.